1. Field of the Invention
This invention relates to a PCM (Pulse Code Modulation) signal processor and particularly to a PCM signal processor in which when reproducing an audio PCM signal, the timing of the reproduced PCM data is stabilized with a specific synchronizing signal.
2. Description of the Prior Art
A known PCM recording and reproducing apparatus has been proposed in which analog and audio signals such as music are converted to an audio PCM signal, to which an error-correction code and an error-detection code are added. The signal is then converted to the same signal format as a television signal which is then recorded or reproduced with a VTR (Video Tape Recorder). Dropout can be caused by dust or the like on a magnetic tape which is used as the recording medium in the VTR; it is possible that a burst error may occur in the recorded PCM signal. If such burst error occurs, it becomes quite difficult to error-correct the lost data. To cope with this problem, in a PCM processor for converting the audio PCM signal to a quasi-video signal, the following arrangement has been proposed. After converting the audio PCM signal to a video signal, during recording, parity data for the PCM data and error-correction are separated for each plurality of words to form a block, and each word of such block is delayed by different times so as to disperse the data to provide interleaving. Upon converting the video signal to the audio PCM signal, during reproducing, a reverse operation (de-interleaving) is carried out and the burst error is dispersed, thereby to correct the data. For delayed processing of the interleaving and the de-interleaving, there is employed a RAM (Random Access Memory). For editing a plurality of different PCM data, the video signal reproduced from a reproducing VTR is recorded by a recording VTR, which may cause deterioration of the tone or data quality. In order to prevent such deterioration, once the video signal derived from the reproducing VTR is converted to the audio PCM signal and after error-corrected, the audio PCM signal is again converted to the video signal, and then recorded on the recording VTR.
In practice, in order to perform cross-fade treatment to smoothly connect two data elements to each other at a editing point or to decide the editing point with higher accuracy than the frame accuracy, the operating modes of the editing system are quite complicated. During editing to determine the editing point and to do the editing, it is necessary that timing to produce the data recorded at a certain specified position from the reproducing circuit of the PCM processor not be changed at each initiation of reproducing operations. However, in a known apparatus, each time the reproducing VTR is driven, the timing to write the reproduced data in the RAM of the processor will be different from each other, thus making editing quite difficult.